1. Field of the Invention
This invention relates to a reproducing apparatus and method, and more particularly to a reproducing apparatus and method for reproducing an optical disk on which a plurality of recording layers of data recorded thereon are read from one face.
2. Description of the Related Art
Optical disks such as compact disks on which data are optically recorded have met with great success and consequently are now widely distributed. The success of such optical disks is due in part to their ability to store large amounts of data in sectors arranged in circumferential tracks.
Recently, a DVD (Digital Versatile Disk) has been developed which is an optical disk having an even larger capacity than its predecessor. The single layer DVD, which was originally proposed, has a single recording layer much like the compact disk. More recently, there has been proposed a dual layer DVD which has two recording layers readable from one face thereof. Such a dual layer DVD, which is capable of storing twice the data, need not be manually turned over since the data is reproduced from the same face.
When reproducing data from any of the optical disks described above, an optical pickup irradiates laser light upon pits etched along the circumferential tracks of a recording layer. The laser light reflected from the pits, which are shaped corresponding to different types of data, is photo-electrically converted by the optical pickup into a signal representing that data.
In the case of reading data from the single layer DVD, the optical pickup is moved by a motor in a radial direction to the optical disk from a current track to a target track. More particularly, a control circuit calculates, from a current sector address of a current reading out position and a next sector address of the next sector to be read, the number of tracks (movement track number) which the optical pickup must be moved, or "track jumped", to read the next sector. The control circuit then causes the motor to track jump the optical pickup by the movement track number.
In the case of reading data from a dual layer DVD, there has been no commercially adopted method heretofore used for reading from different layers. A method proposed by Applicants of the present invention is described with reference to the flow chart of FIG. 7.
Initially, it is determined whether the optical pickup must be refocused to a different layer. Thus, it is discriminated in step S1 from the target sector address St of the next sector to be read and the current sector address Sc of the current sector that the next sector is in a different recording layer than the current recording layer.
Then, in steps S2-S4, "spurt processing" is commenced, wherein the pickup is track jumped along the current layer to a track position parallel, or normal, to the target position in the target recording layer. In step S2, the number of tracks over which the reading out position of the optical pickup must be moved (movement track number) is calculated from the target sector address St and the current sector address Sc. It is discriminated in step S3 whether the movement track number is 0 which means that the current reading out position is already aligned with the target track. Otherwise, the reading out position of the optical pickup is track jumped in step S4 the number of tracks indicated by the movement track number. Whereupon, steps S2 to S4 are repeated until the movement track number is equal to 0.
At this time, the optical pickup is aligned with the target track. But before refocusing the optical pickup to the target layer, servoing must be halted since the optical pickup is not focused on a track during refocusing. To explain, servoing actively controls the speed set by the spindle motor of the optical disk in synchronization with a sampling rate of the optical pickup, the position of the optical pickup set by the motor, and tracking of the optical pickup to the disk. It would be meaningless to perform such servoing when the optical pickup is not focused on a recording layer.
Hence, in step S5, the spindle motor which rotates the optical disk is set to rough servoing, whereby the speed of the rotating optical disk is set to a fixed linear velocity. In step S6, both the servoing control of the motor for moving the optical pickup in a radial direction of the optical disk and the tracking servo control of the optical pickup are halted.
While servoing is halted, the optical pickup is refocused to the target recording layer. More particularly, the distance between the objective lens of the pickup and the target layer optical disk is changed in step S7, thereby refocusing the pickup to the target recording layer
Then, when the optical pickup is focused on the target recording layer, servoing control of the motor is resumed, and the optical disk is rotated with a linear velocity in synchronization with a sampling rate of the optical pickup. Further, tracking servo control is resumed, thereby tracking the optical pickup to the disk.
As a measure to check whether the optical pickup is focused on the target layer, the sector address and the layer information are read out from the optical disk in step S9. Then in step S10, it is discriminated from the layer information whether the recording layer being currently read includes the target sector. If this is not the case, control returns to step S5 where the refocusing procedure in steps S5 to S10 is repeated until the read out position is set to the target recording layer. Control then advances to steps S11 to S13. It is seen that control advances directly to steps S11 to S13 when it is determined in step S1 that the optical pickup does not need to be refocused to a different layer.
Since servoing is halted during refocusing, the track position of the optical pickup may have drifted appreciably. Thus, in steps S11 to S13, spurt processing is again commenced. Thus, the movement track number is calculated in step S11 from the target sector address St and the current sector address Sc. In step S12, it is discriminated whether the movement track number is 0 which means that the optical pickup tracks the target track. Otherwise, the optical pickup must be track jumped by the movement track number as directed by step S13. Control then returns to steps S11 to S13 until the movement track number is 0.
At this time, the optical pickup tracks the target track in the target recording layer, and control advances to step S14 where servo control of the phase of the spindle motor is resumed and control ends.
The movement of the optical disk from the current recording layer to the target recording layer is illustrated in FIG. 8 wherein the reading out position is first moved according to spurt processing (steps S2 to S4) from the current position in the current recording layer (0) toward the target position. Then, the optical disk is refocused from the current recording layer (0) to the target recording layer (1) (steps S5 to S10).
Since the optical pickup may deviate appreciably from the target sector after refocusing in steps S5 to S10 because servoing was halted, spurt processing should be performed a second time in steps S11 to S13. Thus, much time is required for moving the optical pickup to a different recording layer when reproducing a dual layer DVD.